Particulate filter regeneration in an engine

ABSTRACT

Systems and methods for controlling regeneration of a particulate filter positioned downstream of an engine in a vehicle are provided herein. One exemplary method includes, during combusting engine conditions, directing exhaust from the engine to a three-way catalyst and then to a particulate filter positioned downstream of the three-way catalyst. The method also includes, during non-combusting engine conditions and while the vehicle is in motion, directing fresh ram-air to the particulate filter to regenerate the particulate filter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional PatentApplication No. 61/246,936, entitled “Systems and Methods forControlling Regeneration of Particulate Filter in a Spark-IgnitionEngine,” filed Sep. 29, 2009, the disclosure of which is herebyincorporated by reference in its entirety and for all purposes.

TECHNICAL FIELD

The present application relates to regeneration control of a particulatefilter downstream of an engine in a vehicle.

BACKGROUND AND SUMMARY

During some conditions, turbocharged direct-injection engines maygenerate increased soot. For example, during some conditions, fuel maynot sufficiently mix with air before combustion, for example due toreduced turbulence. Such phenomena may occur when the engine isoperating at high speed and/or high loads.

The inventors herein have recognized that one approach to address suchan issue may be to utilize a particulate filter in the exhaust. However,regeneration of the filter in the exhaust of a spark-ignited engineaimed at stoichiometric emission control raises numerous issues. As justan example, sufficient excess oxygen for regeneration in the exhaust mayresult in increased NOx emissions.

Accordingly, systems and methods for controlling regeneration of aparticulate filter positioned downstream of an engine in a vehicle areprovided herein. One exemplary method includes, during combusting engineconditions, directing exhaust from the engine to a three-way catalystand then to a particulate filter positioned downstream of the three-waycatalyst. The method also includes, during non-combusting engineconditions and while the vehicle is in motion, directing fresh ram-airto the particulate filter to regenerate the particulate filter.

By using ram-air to regenerate the particulate filter, the particulatefilter can be regenerated during vehicle motion. Furthermore, a ram-airentrance to the exhaust passage may be downstream of one or more otheremission control devices, thus reducing an effect of excess oxygen onthe one or more other emission control devices.

The present description addresses various aspects of such regenerationand associated control, including adjusting operation during and/orafter an engine shutdown to enable regeneration under such conditions.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a system in a vehicle.

FIG. 2 is a schematic view of an engine of a vehicle.

FIG. 3 is a flowchart illustrating a method for managing particulatefilter regeneration.

FIG. 4 is a flowchart illustrating a high-level method for controllingparticulate filter regeneration.

FIG. 5 is a flowchart illustrating a method for controlling aparticulate filter regeneration that is carried out during enginerunning.

FIG. 6 is a flowchart illustrating a method for controlling particulatefilter regeneration during an engine shutdown.

FIG. 7 is an exemplary timeline of several engine parameters during aparticulate filter regeneration that beings during engine running andcontinues during an engine shutdown.

FIG. 8 is an exemplary timeline of several engine parameters for aparticulate filter regeneration that is carried out during and after anengine shutdown.

FIG. 9 is a flowchart illustrating a high-level method for controlling aparticulate filter regeneration in a hybrid electric vehicle.

FIG. 10 is a flowchart illustrating a method for controlling particulatefilter regeneration during an engine shutdown in a hybrid electricvehicle.

FIG. 11 is an exemplary timeline of several engine parameters during aparticulate filter regeneration that begins during engine running and iscontinued during engine shutdown in a hybrid electric vehicle.

FIG. 12 is an exemplary timeline of several engine parameters during aparticulate filter regeneration carried out during and after an engineshutdown in a hybrid electric vehicle.

FIG. 13 is a flowchart illustrating a method for controlling an enginestart after an engine shutdown.

DETAILED DESCRIPTION

Systems and methods for controlling regeneration of a particulate filterdownstream of an engine are provided herein. Exemplary systems forcontrolling regeneration are schematically illustrated in FIG. 1 andFIG. 2, and the systems may each include a three-way catalyst and aparticulate filter in an exhaust passage downstream of the engine.

In order to carry out a particulate filter regeneration, excess oxygenmay be delivered to the particulate filter, where excess oxygen is anamount of oxygen that is greater than an amount of oxygen deliveredduring normal engine running when an air-fuel ratio is aboutstoichiometric. However, excess oxygen in an exhaust passage maysaturate an oxygen storage capacity of a three-way catalyst, becausethree-way catalysts have a limited amount of oxygen storage. Thus, ifthe engine is running during a period in which the three-way catalyst issubject to excess oxygen (e.g., during particulate filter regeneration),NOx emissions may increase. Accordingly, in order to carry outparticulate filter regeneration without degraded emission controloperation of the three-way catalyst, particulate filter regeneration maybe carried out during at least some engine shutdown and/or engine restconditions, thereby reducing potential NOx emissions. Various examplemethods for such operation are provided herein.

Specifically, FIG. 3 illustrates a method for requesting regenerationand, if so, determining under what conditions a regeneration should becarried out. For example, a regeneration may be carried out when anengine is running, during an engine shutdown, or some combinationthereof. The routine of FIG. 4 includes carrying out the requestedregeneration during the correspondingly selected conditions. The routineof FIG. 5 illustrates an example method for controlling regenerationduring engine running, whereas FIG. 6 illustrates an example method forcontrolling regeneration during an engine shutdown and/or at enginerest. Thereafter, an example timeline of several operating parameters ispresented by way of FIG. 7, which is an example of particulate filterregeneration that begins during engine running and continues through anengine shutdown. FIG. 8 is a second example timeline of severaloperating parameters during a particulate filter regeneration that isinitiated at engine shutdown.

FIG. 9 illustrates a high-level method for determining when to performparticulate filter regeneration in a hybrid electric vehicle (HEV). FIG.10 specifically illustrates a method for controlling regeneration duringan engine shutdown in an HEV. An example timeline of various operatingparameters during a particulate filter regeneration that begins duringengine running in an HEV is illustrated by FIG. 11, and a second exampletimeline of particulate filter regeneration that begins during engineshutdown (e.g., after a decision to stop engine combusting) is shown byFIG. 12.

Finally, FIG. 13 is a flowchart of a method for starting an engine,which may or may not be in an HEV, after an engine shutdown.

Referring now to FIG. 1, the figure schematically depicts a system 100including an internal combustion engine 10, which is a direct-injection,spark-ignition engine in some examples. The engine 10 may have aplurality of cylinders, and engine output torque may be transmitted to atransmission (not shown), which may be, in turn, coupled to a drivewheel in contact with a road surface. The transmission may be a manualtransmission, automatic transmission, or combinations thereof. Further,various additional components may be included, such as a torqueconverter, and/or other gears such as a final drive unit, etc.

The system 100 includes a turbocharger including a turbine 164downstream of the engine 10 and a compressor 162 upstream of the engine10. A throttle 62 for controlling air intake into the intake manifold 44is shown positioned downstream of the compressor 162. In other examples,the throttle 62 may be positioned upstream of the compressor 162, and/oradditional throttles may be provided.

The system 100 is also equipped with a high-pressure (HP) EGR passage140 having a first opening downstream of the throttle 62 and upstream ofcylinders of the engine 10, and a second opening downstream of theturbine 164 and upstream of a particulate filter (PF) 72, by whichexhaust gas can be recirculated. A high-pressure (HP) EGR valve 142 ispositioned between the first opening and second opening of the HP EGRpassage 140, and can be positioned based on current engine operatingconditions. For example, the HP EGR valve 142 may be open during enginerunning when engine boost from the turbocharger is not desired.

The system 100 may also include a low-pressure EGR conduit 26 having alow-pressure (LP) EGR valve 28. The low-pressure EGR conduit 26 mayre-circulate gas from an opening downstream of a three-way catalyst(TWC) 71 to a position upstream of the compressor 162, for example, whenengine boost is desired and/or being carried out by the turbocharger,and while the HP EGR valve 142 is closed.

The engine 10 may be configured to output exhaust, via exhaust passage48, to the TWC 71 positioned downstream of the engine 10. One or moreexhaust sensors may be positioned in exhaust passage 48. For example, anoxygen sensor 14 and a temperature sensor 16 are positioned downstreamof the TWC 71 to measure excess oxygen and temperature, respectively.There may be additional oxygen and temperature sensors upstream of,downstream of, or coupled to each of the TWC 71 and the particulatefilter 72. Excess oxygen may be expressed as a percentage of oxygen inan airflow in the exhaust passage 48. The TWC 71 may be positionedupstream of the particulate filter 72 in order to reduce emissions sothat soot and other particulates received at the particulate filter 72are largely inert.

The system 100 may further include a ram-air conduit 22 having an outletupstream of the particulate filter 72, and configured to direct freshram-air into the _(exhaust passage) 48 upstream of the PF 72 when thevehicle is moving. Specifically, an opening of a ram-air flow valve 24may be selectively controlled to increase or decrease the flow of freshram-air into the exhaust passage 48, thereby affecting an amount ofexcess oxygen in the _(exhaust passage) 48. With this configuration,fresh air can be drawn to the particulate filter 72 while bypassing theTWC 71.

In one example embodiment, an energy conversion device 18 is coupled tothe engine 10. The energy conversion device 18 may include a motor, or agenerator, among others and combinations thereof. The energy conversiondevice 18 is further shown coupled to an energy storage device 20, whichmay include a battery, a capacitor, a flywheel, a pressure vessel, etc.The energy conversion device 18 can be operated to absorb energy fromvehicle motion and/or the engine and convert the absorbed energy to anenergy form suitable for storage by the energy storage device 20 (e.g.,provide a generator operation). The energy conversion device 18 can alsobe operated to supply an output (power, work, torque, speed, etc.) tothe drive wheels and/or engine 10 (e.g., provide a motor operation tokeep engine spinning while not combusting). It should be appreciatedthat the energy conversion device 18 may, in some embodiments, includeonly a motor, only a generator, or both a motor and generator, amongvarious other components used for providing the appropriate conversionof energy between the energy storage device and the vehicle drive wheelsand/or engine.

Connections between engine 10, energy conversion device 18, thetransmission, and drive wheel transmit mechanical energy from onecomponent to another, whereas connections between the energy conversiondevice 18 and the energy storage device 20 may transmit a variety ofenergy forms such as electrical, mechanical, etc. For example, torquemay be transmitted from engine 10 to drive the vehicle drive wheels viathe transmission and, as described above, energy conversion device 18may be configured to operate in a generator mode and/or in a motor mode.In a generator mode, energy conversion device 18 absorbs some or all ofthe output from engine 10 and/or transmission, which reduces the amountof engine output delivered to the drive wheel, or the amount of brakingtorque to the drive wheel. Such operation may be employed, for example,to achieve efficiency gains through regenerative braking, improvedengine efficiency, etc. Further, the output received by the energyconversion device 18 may be used to charge energy storage device 20. Inmotor mode, the energy conversion device 18 may supply mechanical outputto engine 10 and/or transmission, for example by using electrical energystored in an electric battery (e.g., energy storage device 20).

Hybrid-electric propulsion embodiments may include full hybrid systems,in which the vehicle can run on just the engine, just the energyconversion device (e.g., the motor), or a combination of both. Assist ormild hybrid configurations may also be employed, in which enginecombustion is the primary torque source, with the hybrid propulsionsystem acting to selectively deliver added torque, for example duringtip-in or other conditions. Further still, starter/generator and/orsmart alternator systems may also be used.

From the above, it should be understood that the exemplaryhybrid-electric propulsion system is capable of various modes ofoperation. In a full hybrid implementation, for example, the propulsionsystem may operate using energy conversion device 18 (e.g., an electricmotor) as the only torque source spinning the engine and/or propellingthe vehicle. This “electric only” mode of operation may be employedduring braking, low speeds, while stopped at traffic lights, etc. Inanother mode, engine 10 is running (e.g., combusting), and acts as theonly torque source powering drive wheel. In still another mode, whichmay be referred to as an “assist” mode, the energy conversion device 18may supplement and act in cooperation with the torque provided by enginecombustion. As indicated above, energy conversion device 18 may alsooperate in a generator mode, in which torque is absorbed from engine 10and/or transmission.

One or more components discussed with respect to FIG. 1 (e.g., HP EGRvalve, LP EGR valve, turbine wastegate valve, compressor valved bypass,throttle, tailpipe valve, etc.) can be manipulated by an electroniccontroller. In some examples, an objective of such manipulation mayinclude controlling an amount or rate of excess oxygen flow directed tothe particulate filter, and/or a temperature of exhaust gas. Such anelectronic controller is discussed in detail with respect to FIG. 2.

Turning now to FIG. 2, a schematic diagram illustrates one cylinder ofmulti-cylinder engine 10, which may be included in a propulsion systemof an automobile. Engine 10 may be controlled at least partially by acontrol system including controller 12 and by input from a vehicleoperator 132 via an input device 130. In this example, input device 130includes an accelerator pedal and a pedal position sensor 134 forgenerating a proportional pedal position signal PP. Combustion chamber(i.e., cylinder) 30 of engine 10 may include combustion chamber walls 32with piston 36 positioned therein. In some embodiments, the face ofpiston 36 inside cylinder 30 may have a bowl. Piston 36 may be coupledto crankshaft 40 so that reciprocating motion of the piston istranslated into rotational motion of the crankshaft. Crankshaft 40 maybe coupled to at least one drive wheel of a vehicle via an intermediatetransmission system. Further, a starter motor may be coupled tocrankshaft 40 via a flywheel to enable a starting operation of engine10.

Combustion chamber 30 may receive intake air from intake manifold 44 viaintake passage 42 and may exhaust combustion gases via exhaust passage48. Intake manifold 44 and exhaust passage 48 can selectivelycommunicate with combustion chamber 30 via a respective intake valve 52and exhaust valve 54. In some embodiments, combustion chamber 30 mayinclude two or more intake valves and/or two or more exhaust valves.

Intake valve 52 may be controlled by controller 12 via electric valveactuator (EVA) 51. Similarly, exhaust valve 54 may be controlled bycontroller 12 via EVA 53. Alternatively, the variable valve actuator maybe electro hydraulic or any other conceivable mechanism to enable valveactuation. During some conditions, controller 12 may vary the signalsprovided to actuators 51 and 53 to control the opening and closing ofthe respective intake and exhaust valves. The position of intake valve52 and exhaust valve 54 may be determined by valve position sensors 55and 57, respectively. In alternative embodiments, one or more of theintake and exhaust valves may be actuated by one or more cams, and mayutilize one or more of cam profile switching (CPS), variable cam timing(VCT), variable valve timing (VVT) and/or variable valve lift (VVL)systems to vary valve operation. For example, cylinder 30 mayalternatively include an intake valve controlled via electric valveactuation and an exhaust valve controlled via cam actuation includingCPS and/or VCT.

Fuel injector 66 is shown coupled directly to combustion chamber 30 forinjecting fuel directly therein in proportion to the pulse width ofsignal FPW received from controller 12. In this manner, fuel injector 66provides what is known as direct injection of fuel into combustionchamber 30. The fuel injector may be mounted in the side of thecombustion chamber or in the top of the combustion chamber, for example.Fuel may be delivered to fuel injector 66 by a fuel system (not shown)including a fuel tank, a fuel pump, and a fuel rail.

An ignition system (not shown) can provide an ignition spark tocombustion chamber 30 via a spark plug in response to a spark advancesignal from controller 12, under select operating modes. Under someconditions or in some embodiments, compression ignition may be carriedout without a spark ignition.

Intake passage 42 or intake manifold 44 may include a throttle 62 havinga throttle plate 64. In this particular example, the position ofthrottle plate 64, or a throttle opening, may be varied by controller 12via a signal provided to an electric motor or actuator included withthrottle 62, a configuration that is commonly referred to as electronicthrottle control (ETC). In this manner, throttle 62 may be operated tovary the intake air provided to combustion chamber 30 among other enginecylinders. The position of throttle plate 64 may be provided tocontroller 12 by throttle position signal TP. Intake passage 42 mayinclude a mass airflow sensor 120 and a manifold air pressure sensor 122for providing respective signals MAF and MAP to controller 12.

Further, in the disclosed embodiments, an exhaust gas recirculation(EGR) system may route a desired portion of exhaust gas from exhaustpassage 48 to intake manifold 44. In this example, an HP EGR passage 140is illustrated. The amount of EGR provided to intake manifold 44 may bevaried by controller 12 via HP EGR valve 142. Further, an EGR sensor 144may be arranged within the HP EGR passage 140 and may provide anindication of one or more of pressure, temperature, and concentration ofthe exhaust gas. Alternatively, the EGR flow may be controlled through acalculated value based on signals from the MAF sensor (upstream), MAP(intake manifold), MAT (manifold gas temperature) and the crank speedsensor. Further, the EGR flow may be controlled based on an exhaust O₂sensor and/or an intake oxygen sensor (intake manifold). Under someconditions, the EGR system may be used to regulate the temperature ofthe air and fuel mixture within the combustion chamber and/or thetemperature at a particulate filter, as will be discussed. While FIG. 2shows a high pressure EGR system, a low pressure EGR system mayadditionally, or alternatively, be used. In a low pressure EGR system,EGR may be routed from downstream of a turbine of a turbocharger toupstream of a compressor of the turbocharger, as show in FIG. 1.

As such, engine 10 may further include a compression device such as aturbocharger or supercharger including at least a compressor 162arranged along intake manifold 44. For a turbocharger, compressor 162may be at least partially driven by a turbine 164 (e.g., via a shaft)arranged along _(exhaust passage) 48. For a supercharger, compressor 162may be at least partially driven by the engine 10 and/or an electricmachine, and may not include a turbine. Thus, the amount of compressionprovided to one or more cylinders of the engine via a turbocharger orsupercharger may be varied by controller 12.

Exhaust gas sensor 126 is shown coupled to exhaust passage 48 upstreamof emission control system 70. Exhaust gas sensor 126 may be anysuitable sensor for providing an indication of exhaust gas air/fuelratio such as a linear oxygen sensor or UEGO (universal or wide-rangeexhaust gas oxygen), a two-state oxygen sensor or EGO, a HEGO (heatedEGO), a NOx, HC, or CO sensor. Although oxygen sensor 14 and temperaturesensor 16 are shown in addition to exhaust gas sensor 126 in FIG. 2, oneor more of these sensors may be omitted and/or moved.

The emission control system 70 is shown arranged along exhaust passage48 downstream of exhaust gas sensor 126. In this example, emissioncontrol system 70 includes the three-way catalyst 71 and the particulatefilter (PF) 72. In some embodiments, PF 72 may be located downstream ofthe three-way catalyst 71 (as shown in FIG. 2), while in otherembodiments, PF 72 may be positioned upstream of the catalyst (not shownin FIG. 2). Further, PF 72 may be arranged between two or more three-waycatalysts, or other emission control devices (e.g., selective catalyticreduction system, NOx trap) or combinations thereof. During operation ofengine 10, components of the emission control system 70 may beperiodically reset by operating at least one cylinder of the enginewithin a particular air/fuel ratio.

Controller 12 is shown in FIG. 2 as a microcomputer, includingmicroprocessor 102, input/output ports 104, an electronic storage mediumfor executable programs and calibration values shown as read-only memory106 in this particular example, random access memory 108, keep alivememory 110, and a data bus. Controller 12 may receive various signalsfrom sensors coupled to engine 10, in addition to those signalspreviously discussed, including measurement of inducted mass airflow(MAF) from mass airflow sensor 120; engine coolant temperature (ECT)from temperature sensor 112 coupled to cooling sleeve 114; a profileignition pickup signal (PIP) from Hall effect sensor 118 (or other type)coupled to crankshaft 40; throttle position (TP), or throttle opening,from a throttle position sensor; and absolute manifold pressure signal,MAP, from sensor 122. Engine speed signal, RPM, may be generated bycontroller 12 from signal PIP. Manifold pressure signal MAP from amanifold pressure sensor may be used to provide an indication of vacuum,or pressure, in the intake manifold. Note that various combinations ofthe above sensors may be used, such as a MAF sensor without a MAPsensor, or vice versa. During stoichiometric operation, the MAP sensorcan give an indication of engine torque. Further, this sensor, alongwith the detected engine speed, can provide an estimate of charge(including air) inducted into the cylinder. In one example, sensor 118,which is also used as an engine speed sensor, may produce apredetermined number of equally spaced pulses every revolution of thecrankshaft.

Storage medium read-only memory 106 can be programmed with computerreadable data representing instructions executable by microprocessor 102for performing the methods described herein, as well as other variantsthat are anticipated but not specifically listed.

As described above, FIG. 2 shows only one cylinder of a multi-cylinderengine, and each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector, spark plug, etc.

Now, particulate filter regeneration control will be described indetail. Turning to FIG. 3, the flowchart illustrates an exemplary method300 for managing particulate filter regeneration. At 302, an engineshutdown regeneration flag and an engine running regeneration flag areinitially set to zero. At 304, an amount of particulate, or soot, storedat a particulate filter is estimated by an electronic controller, forexample. This may be achieved by measuring a backpressure value, such asa change in backpressure in the exhaust, and matching the backpressurevalue to an amount of particulate using a table or calculation stored atan electronic controller. At 306, it is determined if the estimatedamount of particulate is greater than a first threshold amount,T_(SHUTDOWN). If the answer is no at 306, and the amount of particulateis below the first threshold amount T_(SHUTDOWN), the method 300 isterminated. If the answer is yes at 306, the engine shutdownregeneration flag is set equal to one at 308, indicating that aregeneration during engine shutdown is desirable when conditions areappropriate for doing so.

At 310, it is determined if an amount of particulate, or soot, at theparticulate filter is greater than a second threshold amount,T_(RUNNING). If the answer is no at 310, and the amount of particulateis greater than T_(SHUTDOWN) and less than T_(RUNNING), the method 300may be terminated, and the engine shutdown regeneration flag may beequal to one until an engine shutdown regeneration is at least partiallycompleted, or until the amount of particulate is less than T_(SHUTDOWN),in some examples.

If the answer is yes at 310, and the amount of particulate, or soot, isgreater than T_(RUNNING), the engine running regeneration flag may beset equal to one at 312, indicating that an engine running regenerationis desirable when conditions are next appropriate for doing so. As such,the engine running regeneration flag may be equal to one until an enginerunning regeneration (e.g., regeneration during at least partial enginecombusting conditions) is carried out, or until the amount ofparticulate is less than T_(RUNNING).

An engine shutdown regeneration of the particulate filter may be apartial regeneration because it may not fully rid the particulate filterof particulate, or soot. As such, the first threshold amountT_(SHUTDOWN) may be less than the second threshold amount T_(RUNNING) insome examples. However, there may also be conditions where it isdesirable to carry out an engine running regeneration when the firstthreshold amount T_(SHUTDOWN) is met and the second threshold amountT_(RUNNING) is not met, such as when conditions are appropriate forperforming an engine running particulate filter regeneration and thereare substantially inconsequential effects of doing so. Further, theremay be conditions where an engine shutdown regeneration is capable offully regenerating the particulate filter, such that when both of thethresholds T_(SHUTDOWN) and T_(RUNNING) are met, an engine shutdownregeneration is carried out.

It is notable that a method for determining whether or not to carry outa particulate regeneration, or when to carry out a particulate filterregeneration, may take various forms, and that method 300 of FIG. 3 ismerely exemplary.

In general, spark-ignition engines accumulate soot in the exhaust,especially under high load, boosted conditions. However, it is desirableto combust spark-ignition engines with about-stoichiometric air-fuelratios (e.g., air-fuel ratios which oscillate about stoichiometric) inorder to prevent high NOx emissions from a three-way catalyst downstreamof the engine. In contrast to a lean-burn diesel engine, aspark-ignition engine may not be configured to regularly provide excessoxygen (e.g., a percentage of oxygen above that provided when operatingabout stoichiometry) in the exhaust during engine combusting conditions.As a result, some methods for controlling regeneration of a dieselparticulate filter during engine running may not be applicable forregeneration control of a particulate filter in a spark-ignition engine.Further still, it can be challenging to achieve a high temperature atwhich a regeneration reaction can be carried out at a particulate filterwhile still maintaining control of the regeneration reaction in aspark-ignition engine.

To address some of these challenges, a high-level method 400 forcontrolling particulate filter regeneration during engine running andduring engine shutdown in a spark-ignition engine is illustrated in FIG.4. The method 400 is described generally and may thus apply tonon-hybrid electric vehicles as well as hybrid electric vehicles.

At 402, it is determined if an engine shutdown has been requested. Anengine shutdown request may be indicated, for example, when an engine iscombusting and an operator turns off an ignition switch. As anotherexample, an engine shutdown may be requested during conditions for adeceleration fuel shut-off operation. If the answer is no at 402, it isdetermined at 404 if the engine running regeneration flag is equal toone. If the answer is yes, and an engine running regeneration isdesirable, the method 400 includes regenerating the particulate filterduring engine running at 406, which is described in detail with respectto method 500 of FIG. 5.

However, if the answer is no at 404, such that an engine runningregeneration flag is equal to zero, or engine running regeneration isnot desirable, the method 400 may be terminated.

If the answer is yes at 402, such that an engine shutdown is requested,the method 400 proceeds to 408, where it is determined if the engineshutdown regeneration flag is equal to one. If the answer is no at 408,the method may proceed to 410, where an engine shutdown is performedwithout actively performing a particulate filter regeneration. That is,at 410, actions may not be taken to initiate, facilitate, or prolongparticulate filter regeneration. It may be desirable to carry out anengine shutdown without active particulate filter regeneration underconditions where particulate filter regeneration may be unsuccessful,and/or when particulate filter regeneration can be delayed withoutcompromising the integrity of the particulate filter.

Accordingly, at 410, the engine shutdown may include setting theair-fuel ratio to about stoichiometry for one or more last combustionsat 412 to reduce excess oxygen to the particulate filter. The one ormore last combustions may refer to combustions in a transition periodbetween the engine shutdown request and the stopping of combustion(e.g., beginning of engine spin-down). This transition period (e.g., oneor more last combustions) may include any number of combustions, forexample in the range of 1-20. In some cases, there may not be atransition period between engine shutdown request and the beginning ofengine spin-down, and there may be no last combustions.

Excess oxygen to the particulate filter may be reduced during an engineshutdown without an active regeneration by reducing the opening of thethrottle, such as at 414. By reducing the opening of the throttle atengine shutdown without regeneration, the exhaust heat may dissipate ata predetermined rate (e.g., faster than during an engine shutdownlacking this step), thereby facilitating cooling of emission controlcomponents (e.g., three-way catalyst, particulate filter). Furthermore,the reduction of excess oxygen at 414 reduces a likelihood ofparticulate filter regeneration. In some examples, reducing the openingof the throttle at 414 may occur during one or more last combustionsand/or during engine spin-down after the engine has stopped combusting.Although actions are taken to reduce excess oxygen directed to theparticulate filter at 410, some particulate filter regeneration mayspontaneously occur.

If the answer is yes at 408, the method 400 proceeds to 416 where it isdetermined if the temperature at the particulate filter is at leastgreater than a baseline temperature threshold T_(THRESH) at the time ofthe engine shutdown request. If the answer is no at 416, regenerationmay be delayed and the engine shutdown regeneration flag remains equalto one while the method 400 proceeds to 410 for an engine shutdownwithout an active regeneration. This may occur, for example, if anengine shutdown is performed in the midst of an engine cold start, andthe temperature of the particulate filter is so low that a temperaturerequired for a regeneration reaction may not be met even by manipulationof operating parameters during the engine shutdown. That is, thebaseline temperature threshold T_(THRESH) may be a temperature fromwhich a temperature required for the regeneration reaction can be metvia manipulation of operation parameters, and/or within a predeterminedamount of time after engine shutdown request. In this way, failedattempts to regenerate the particulate filter during an engine shutdowncan be prevented and/or reduced. Other parameters indicative ofparticulate filter readiness for regeneration may be checked at 416.

If the answer is yes at 416, and the particulate filter temperature isgreater than T_(THRESH), the method 400 includes actively regeneratingthe particulate filter during engine shutdown at 418, which is describedin detail with respect to method 600 of FIG. 6. Notably in contrast tothe engine shutdown of 410, the engine shutdown of 418 may includeincreasing excess oxygen to the particulate filter by setting the engineto combust with a lean air-fuel ratio and/or by increasing a throttleopening, as just some examples. The particulate filter regeneration of418 may be carried out for at least a portion of engine shutdown.

In general, a regeneration reaction at a particulate filter may occurwhen the particulate filter is subject to particular levels of excessoxygen and particular temperature conditions. The excess oxygen andtemperature at a particulate filter affect one another, and thus, bothare actively controlled in order to carry out a regeneration reaction.As one example, some particulate filters will begin the regenerationreaction at a substantial rate when the temperature is at least 600degrees F. and there is sufficient excess oxygen. The particulate filterregeneration reaction is exothermic, so once the reaction begins, thetemperature may rapidly increase unless the excess oxygen is carefullycontrolled. For example, if the temperature exceeds a high temperaturethreshold, the reaction may become uncontrollable and can actually stopaltogether as a level of excess oxygen needed for a high temperatureregeneration cannot be supplied. Furthermore, if an amount of excessoxygen is too low at the particulate filter, the regeneration reactionmay be unable to sustain itself. Further still, if excess oxygen levelsare too high, the particulate filter may be cooled, and the regenerationreaction may slow down.

It may be appreciated that when a decision to perform engine shutdownregeneration occurs, such as at 418 of method 400, a regenerationreaction may already be being carried out at the particulate filter(e.g., during engine combustion, or engine running). Thus, theregeneration may be continued through the transition period to engineshutdown. An example of continuing regeneration from engine combustionconditions to engine shutdown conditions is described later, withrespect to FIG. 7. If a regeneration reaction is already being carriedout at the particulate filter at 416 of method 400, it is likely thatthe temperature of the particulate filter is greater than T_(THRESH) andstep 416 may be skipped. In another example, However, even if the answeris no at 408, but a regeneration reaction is already being carried out,the method 400 may proceed to 418 to finish, or continue theregeneration of the particulate filter.

Turning now to FIG. 5, a flowchart illustrates a method 500 forcontrolling a particulate filter regeneration during engine running. Anengine running regeneration may include a regeneration that begins whileat least one cylinder of the engine is combusting, and where a decisionto shut down the engine has not been made.

At 502, the method 500 includes increasing excess oxygen at theparticulate filter. While an engine is combusting, exhaust may bedirected from the engine to a three-way catalyst, and then to aparticulate filter downstream of the three-way catalyst. Thus, because athree-way catalyst may be subject to exhaust output from the engine, itis advantageous to maintain the air-fuel ratio of the combusting engineabout stoichiometry to reduce emissions during engine running (e.g. at502).

As such, the increasing of excess oxygen to the particulate filter at502 may include, at 504, increasing an opening of a ram-air flow valve,such as ram-air flow valve 24 presented in FIG. 1. In this way, anamount of ram-air introduced into the exhaust passage upstream of aparticulate filter can be increased as long as the vehicle is moving,and excess oxygen at the particulate filter can be increased to a levelneeded for regeneration, without increasing emissions at the three-waycatalyst. It is notable that, during combusting engine conditions whilethe vehicle is in motion, ram-air may be introduced to the exhaust basedon the pressure of the exhaust passage being below a threshold pressurevalue. When the pressure differential between ram-air and an exhaustpassage is sufficiently high, the ram-air can be pushed into or drawninto the exhaust by that pressure differential. Accordingly, it may beprudent to close a ram-air flow valve based on a pressure of an exhaustpassage exceeding a threshold pressure value, during some combustingengine conditions while the vehicle is in motion.

At 504 of method 400, fresh air may alternatively or additionally bepumped into the exhaust passage via a mechanical or electrical pump, ora vacuum may be created in the exhaust passage, and fresh air can besucked into the exhaust passage thereafter.

Excess oxygen to the particulate filter can also be increased at 502 bymanipulating the air-fuel ratio oscillations in the cylinders in such amanner that emissions from the three-way catalyst are maintained at alow level. For example, a lean duration can be increased, a richduration can be reduced, or oscillation amplitude can be increased inorder to increase excess oxygen in the exhaust. Furthermore, if ram-airis being introduced into the exhaust passage by vehicle motion, air-fuelratio parameters may be adjusted based on a vehicle speed. For example,as a vehicle speed decreases, lean duration may be increased and/or richduration may be decreased, to compensate for a potential decrease inram-air flow. Similarly, as a vehicle speed increases, a rich durationmay be increased, lean duration may be decreased, and/or oscillationamplitude may be decreased, to compensate for an expected increase inram-air flow. In this way, the air-fuel ratio oscillations cancompensate for increases and decreases in fresh air at the particulatefilter that are due to changes in vehicle speed. However, it may beappreciated that an adjustment of an air-fuel ratio for the purpose ofincreasing excess oxygen to the particulate filter may be further basedon potential or actual emissions from a three-way catalyst positionedupstream of the particulate filter.

The method 500 may also include increasing exhaust heat to theparticulate filter at 506 so that the particulate filter can be heatedto a temperature at which the regeneration reaction can take place at adesired rate. Increasing exhaust heat may include retarding spark timingand/or increasing a throttle opening at 508, which will, in turn,increase an air charge volume and exhaust heat. Exhaust heat can also,or alternatively, be increased by increasing engine speed or load.

At 510, the method 500 may include adjusting excess oxygen levels at theparticulate filter, and/or adjusting particulate filter temperatureduring the regeneration reaction, to sustain the regeneration reaction.In some examples, the excess oxygen levels are adjusted based onfeedback from an oxygen sensor upstream of the particulate filter.

Specifically, excess oxygen levels can be controlled during enginerunning regeneration by adjusting various operating parameters. Theseoperating parameters may include a throttle opening, an air-fuel ratio,variable cam timing, and/or a ram-air flow valve opening, as just someexamples. For example, in order to reduce excess oxygen at theparticulate filter, a throttle opening may be reduced, an air-fuel ratioof one or more cylinders may be made richer (or a rich duration of anoscillation can be made longer), and/or an amount of fresh air suppliedto the exhaust may be reduced.

Furthermore, ram-air may be independently controlled based on vehiclespeed, so that as the vehicle speed increases, an opening of the ram-airflow valve decreases and as the vehicle speed decreases, the opening ofthe ram-air flow valve increases, in order to maintain a steady streamof ram-air in the exhaust passage. In order to increase excess oxygen atthe particulate filter, a throttle opening may be increased, air-fuelratio may be made leaner, and/or an amount of ram-air supplied to theexhaust may be increased based on vehicle speed. For example, if excessoxygen levels start to decline at the particulate filter, the ram-airflow valve opening can be increased to rapidly result in increasedexcess oxygen, if the vehicle is moving.

To decrease excess oxygen levels, a ram-air flow valve opening may bereduced, a throttle opening may be reduced and/or engine speed may bereduced, as some examples. By reducing excess oxygen levels, theexothermic regeneration reaction rate may slow down and the particulatefilter may resultantly cool down.

Temperature can be adjusted at 510 based on feedback from a temperaturesensor positioned at the particulate filter, or elsewhere in the exhaustpassage. The particulate filter temperature can be adjusted duringengine running regeneration by adjusting various operating parameters,such as spark timing, engine speed, and/or excess oxygen levels (e.g.,by controlling throttle opening, air-fuel ratio, ram-air flow valveopening). For example, if the particulate filter temperature begins todecrease below a low temperature threshold at which the regenerationreaction will not be sustained at a desired rate, spark timing can benominally retarded, throttle opening can be increased and/or enginespeed can be increased (or decreased, based on the nominal exhausttemperature and engine speed) to increase exhaust heat. Also, in orderto increase exhaust heat during engine running, excess oxygen may beincreased or decreased, based on the nominal exhaust temperature. On theother hand, if the particulate filter temperature begins to increaseabove a high temperature threshold, such that sufficient excess oxygenlevels may not be supplied for the regeneration reaction at thattemperature, the particulate filter temperature may be reduced bydecreasing the excess oxygen levels and/or by advancing spark timing.Additionally, engine speed can be decreased (or increased) in order toreduce particulate filter temperature.

Turning now to FIG. 6, a flowchart illustrates method 600 forcontrolling particulate filter regeneration during an engine shutdown.At 602, the method 600 may include increasing excess oxygen at theparticulate filter. Increasing excess oxygen at the particulate filterduring an engine shutdown may include setting an air-fuel ratio to belean in at least one cylinder at 604 for one or more last combustionsbefore engine combustion stops. Thus, the regeneration during engineshutdown may include the one or more last combustions immediately beforethe engine stops combusting. At 606, the method 600 may alternately oradditionally include increasing an opening of a ram-air flow valve, ifthe vehicle is moving. A pressure of ram-air may fluctuate withvariations in vehicle speed. Thus, the ram-air flow valve may beadjusted based on a vehicle speed, to compensate for potential changesin excess oxygen flowing to the particulate filter as a result ofchanges in ram-air pressure. Specifically, this may include adjustingthe ram-air flow valve by increasing an opening of the ram-air flowvalve as vehicle speed decreases, and increasing the opening as vehiclespeed increases.

At 608, the method 600 may include increasing the throttle opening andor an opening of one or more charge motion control valves, during anyportion of the engine shutdown, in order to increase (or maintain)excess oxygen flowing to the particulate filter.

At 610, increasing excess oxygen to the particulate filter may includestopping the engine at a position where the cylinders are closed, orclosing the intake and exhaust valves of the cylinders using EVA forexample, and increasing an opening of a HP EGR valve. This may alsoinclude opening the throttle, and closing an EGR wastegate. In this way,fresh air can be drawn in through the intake manifold, bypass the enginevia the HP EGR passage, and be delivered immediately upstream of thethree-way catalyst (as shown in FIG. 1) or immediately upstream of theparticulate filter (in other examples). By having airflow bypass theengine, airflow resistance is reduced and an inertial airflow in theintake manifold can be taken advantage of, after engine combusting isstopped. This technique takes advantage of existing structure by usingan HP EGR passage—which, during engine running, is used forre-circulating exhaust gas from the exhaust passage to an upstreamportion of the engine—as a bypass conduit in order to more directlydeliver fresh air from upstream of the engine to the particulate filterfor regeneration of the particulate filter.

In another example, where EGR passages are closed or EGR systems areomitted, one or more cylinders may be configured to stop combusting withboth an intake valve and an exhaust valve open (e.g., valve overlap),such that air can be drawn in through the intake manifold and passed tothe particulate filter through the one or more open cylinders to therebyincrease excess oxygen to the particulate filter. In such a case, thethrottle opening may be adjusted to control excess oxygen flowingthrough one or more cylinders and to the particulate filter.

As yet another example of increasing excess oxygen to the particulatefilter, pressure or vacuum may be generated and stored in the intakemanifold, and thereafter be used to push or draw air, respectively,through the particulate filter.

Furthermore, the method 600 may include increasing exhaust heat at 612in order to bring a particulate filter temperature toward a regenerationreaction temperature. This increasing of exhaust heat may be carried outby adjusting spark timing to be more retarded during one or more lastcombustions of engine shutdown at 614, for example. Additionally,exhaust heat may be increased by adjusting an air-fuel ratio to beleaner for one or more last combustions, for example. As discussedabove, engine speed and load may also be adjusted for one or more lastcombustions, in order to manipulate exhaust temperature.

Thus, it can be appreciated that excess oxygen levels may be increasedimmediately after an engine shutdown request by operating lean and/orretarding spark timing, and excess oxygen levels can be maintained atthe particulate filter through engine spin-down and after the enginecomes to a rest.

The regeneration reaction may be controlled at 616 by adjusting variousoperating parameters in efforts to control excess oxygen levels andtemperature at the particulate filter, as discussed above with respectto FIG. 5. For example, if an oxygen concentration in the exhaustpassage is too high (e.g., greater than a high excess oxygen threshold),a throttle opening can be reduced, and if an oxygen concentration at theparticulate filter is too low, throttle opening can be increased.Additionally, during a portion of the engine shutdown while the engineis spinning (e.g., during engine spin-down), the HP EGR valve openingcan be increased or decreased to respectively increase or decrease anamount of excess oxygen directed to the particulate filter.

Furthermore, if a temperature of the particulate filter becomes too low(e.g., less than a low temperature threshold), efforts to increase anamount of excess oxygen may be carried out. If the temperature becomestoo high (e.g., greater than a high temperature threshold), excessoxygen may be decreased to reduce the regeneration reaction rate and/orthe airflow may be increased to cool down the particulate filtertemperature.

An exemplary timeline of several engine parameters during an enginerunning regeneration and an engine shutdown regeneration is illustratedin FIG. 7. The example of FIG. 7 can be understood by the methodspresented by FIG. 5 and FIG. 6.

At t₀, the engine is on and at least one cylinder is combusting (e.g.,partial engine combustion). The air-fuel ratio is set aboutstoichiometry and spark timing is MBT (minimum spark advance for besttorque). Throttle position, excess oxygen at the particulate filter, andparticulate filter temperature are each at initial respective levels.

At t₁, a decision to regenerate the particulate filter during enginerunning is made, and engine running regeneration is initiated (see FIG.5). For example, a ram-air flow valve opening may be increased tothereby increase excess oxygen at the particulate filter. This isreflected by an increase in the excess oxygen between t₁ and t₂. Asdiscussed above, this increase in excess oxygen may be achieved by oneor more techniques, or combinations thereof. Additionally, spark timingis retarded at t₁ to increase the particulate filter temperature toabove minimum temperature T_(LOW) at which a regeneration reaction canbe carried out. In this example, a minimum excess oxygen thresholdO_(LOW), determined based on the current particulate filter temperature,for a regeneration reaction to occur is met at t₂. That is, beforeengine shutdown conditions are met in this example, the particulatefilter may begin regeneration.

At t₃, the particulate filter temperature decreases below the lowtemperature threshold T_(LOW), in one example, due to a low level ofoxygen at the particulate filter. For example, the level of excessoxygen O_(LOW), may be insufficient to sustain the regeneration reactionfor longer than the period of time between t₂ and t₃ at a giventemperature. As such, spark timing is further retarded at t₃ in order toheat the particulate filter. As a result, the particulate filtertemperature begins to rise, and eventually exceeds the low temperaturethreshold T_(LOW) at t₃′. After t₃′, and until t₆, the temperatureremains steadily above T_(LOW) and below a high temperature thresholdT_(HIGH), where T_(HIGH) may be a temperature above which theregeneration reaction is difficult to sustain and/or control. Also,after t₃′ and until t₄, the excess oxygen at the particulate filterstays steadily above O_(LOW) and below O_(HIGH). Spark timing, throttleposition, and engine speed are unchanged between t₃′ and t₄, in thisexample, in order to sustain a desired regeneration reaction rate.However, it may be appreciated that, in other examples, spark timing,throttle position, and/or engine speed may be changed duringregeneration based on other demands on the vehicle, and one or moreother operating parameters may be complementarily adjusted.

At t₄, an engine shutdown request is made (e.g., an operator turns offan ignition switch). In response, the air-fuel ratio is made leaner inorder to increase excess oxygen at the particulate filter. As a result,the excess oxygen at the filter increases at t₄. Although not shown, thetemperature may be affected by such an increase in excess oxygen at theparticulate filter. However, the temperature may be unaffected.Furthermore, although not shown, spark timing may be further retardedafter an engine shutdown request is made, if it is desirable to increaseheat to the particulate filter. In this example of FIG. 7, spark timingis already retarded at t₄, and a regeneration reaction temperature isalready achieved, so the spark retard is simply maintained.

At t₅, engine combustion stops and engine spin-down begins, as indicatedby the air-fuel ratio becoming infinitely lean, and the cessation ofspark timing. Here, the regenerating is continued from regenerationduring engine combustion to regeneration during non-combusting, byincreasing the throttle opening to maintain and/or increase excessoxygen at the particulate filter, even though the engine speed isdecreasing. One or more charge motion control valves (CMCVs) may also beopened to increase excess oxygen at the particulate filter. After t₅,the excess oxygen increases, at least in part due to the increasedthrottle opening and the spinning of the engine.

At t₆, the excess oxygen at the filter exceeds O_(HIGH), thereby causinga cooling of the filter temperature below T_(LOW). In response, thethrottle opening is reduced, and the engine speed continues to decrease,thus resulting in a decrease in excess oxygen at the filter, and anincrease in filter temperature as the regeneration reaction rateincreases at t₆′. Additionally or alternatively, if an HP EGR valve isopen at t₆, and air is bypassing the engine via the HP EGR circuit to bedirected to the particulate filter during engine spin-down, the HP EGRvalve opening may be reduced at t₆ to reduce the flow of air through theEGR conduit. It is notable that temperature is also affected (e.g.,reduced) by the increase in oxygen at t₆.

A regeneration reaction may continue even after the engine spins down,as the regeneration reaction is exothermic, and air (e.g., excessoxygen) may continue to passively reach the particulate filter via aram-air flow valve opening and/or through one or more open cylinders ofthe engine (e.g., a cylinder having valve overlap).

From the examples provided, it can be understood that the increasing ofexcess oxygen to the particulate filter may be carried out while atemperature of the particulate filter is within a prescribed temperaturerange (e.g., between T_(THRESH) or T_(THRESH2) and T_(HIGH)).

Turning now to FIG. 8, a second exemplary timeline of several operatingparameters during a particulate filter regeneration that begins duringan engine shutdown is shown. At t₀ of FIG. 8, the engine is combusting,an air-fuel ratio is set about stoichiometric, and spark timing is MBT(minimum spark advance for best torque). Throttle position, excessoxygen, or oxygen concentration at the filter, and filter temperatureare at initial respective levels.

At t₁, an engine shutdown request is made, and the engine shutdownregeneration flag has been set to be equal to one. As such, aparticulate filter regeneration is to be carried out during engineshutdown. Accordingly, at t₁, the air-fuel ratio is set to be lean,spark timing is nominally retarded during one or more last combustions,and the throttle opening is increased. Accordingly, the excess oxygenincreases sharply, and then gradually along with the increase in filtertemperature after t₁.

At t₂, the engine stops combusting, and engine spin-down begins. Betweent₂ and t₃, the engine spins down while the throttle position remainsopen, to gradually increase the concentration of oxygen directed to theparticulate filter. The particulate filter temperature graduallyincreases upon engine shutdown.

At t₃, the engine speed reduces to zero and the engine is at rest. Alsoat t₃, the excess oxygen at the particulate filter exceeds O_(LOW) andthe filter temperature exceeds T_(LOW), thus placing the particulatefilter under conditions for a regeneration reaction to occur at apredetermined rate. The regeneration reaction ensues until t₄, where thereaction ceases to sustain at the predetermined rate, and the excessoxygen level at the filter decreases to below O_(LOW). The temperaturealso decreases. As a result, the low excess oxygen threshold O_(LOW) forresuming the regeneration reaction at the predetermined rate increases(as indicated by the increase of dotted line O_(LOW)), at least in partdue to the decrease in particulate filter temperature.

In response to the low excess oxygen at the particulate filter, thethrottle position is further increased at t₄. As a result, the excessoxygen level increases to above the new low excess oxygen thresholdO_(LOW) at t₄′, and the regeneration reaction resumes at thepredetermined regeneration reaction rate.

Thus, in this example, the increasing of excess oxygen to theparticulate filter occurs during one or more last combustions and duringengine spin-down, and the actual regeneration reaction occurs at asubstantial rate after the engine spins down to rest, and continuesduring engine rest. Eventually, the regeneration reaction may completeand the regeneration reaction will cease due to inadequate particulateat the particulate filter. Alternately, the regeneration reaction may bestopped due to a decrease in excess oxygen and/or a decrease inparticulate filter temperature at some time during engine rest.

In general, a desired excess oxygen range (e.g., range between O_(LOW)and O_(HIGH)) may change based on a current particulate filtertemperature or based on a desired particulate filter temperature range.For example, if temperature of the particulate filter decreases from anominal particulate filter temperature, during a regeneration reaction,a high excess oxygen threshold may decrease. On the other hand, if theparticulate filter temperature increases from a nominal particulatefilter temperature during a regeneration reaction, a low excess oxygenthreshold may increase. That is, a low excess oxygen threshold and ahigh excess oxygen threshold may be dynamic, and may be based on anominal particulate filter temperature and a nominal amount of excessoxygen at a particulate filter, as well as an amount of particulatestored at the particulate filter.

Particular considerations, and advantages, may be taken into accountwhen performing regeneration of the particulate filter in an HEV, wherean engine can be made to be partially or fully non-combusting withincreased frequency and/or with more flexibility compared to aconventional combustion engine. For example, engine shutdownregeneration can be carried out while an energy conversion device, suchas a motor, provides power to the engine, transmission, and/ordrivewheel. As such, methods for controlling a regeneration of aparticulate filter in a hybrid electric vehicle (HEV) are specificallydescribed with respect to FIG. 9 and FIG. 10, and two example timelinesinvolving particulate filter regeneration in an HEV are shown in FIG. 11and FIG. 12. However, the methods described above, and the examplespresented above, may also be applied for regeneration of a particulatefilter in an HEV.

Turning to the method 900 of FIG. 9, it is determined if engine shutdownconditions are met at 902. Engine shutdown conditions may include abattery state of charge (SOC) above a predetermined charge level, as oneexample. The predetermined charge level may include an amount of chargesufficient for powering an engine, transmission, and/or drivewheel for apredetermined amount of time. Engine shutdown conditions may alsoinclude an engine speed, engine load and/or vehicle speed demand beingbelow a respective threshold. That is, the engine shutdown conditionsmay be met at 902 if the engine speed, engine load and/or vehicle speedare low enough that an energy conversion device can maintain the enginespeed, engine load and/or vehicle speed. In another example, engineshutdown conditions may be met more or less frequently based on fueleconomy objectives of the engine. Furthermore, engine shutdownconditions may be met in some HEVs simply if it is desirable to performa particulate filter regeneration during engine shutdown (e.g., even ifother conditions deem particulate filter regeneration undesirable).

If the answer is no at 902, the method 900 proceeds to 904 where it isdetermined if the engine running regeneration flag is equal to one. Ifthe answer is no, the method 900 may terminate. If the answer is yes at904, the method may proceed to 906, where the particulate filterregeneration may be carried out during engine running. Reader isreferred to the description of method 500 of FIG. 5 for controllingparticulate filter regeneration during engine running.

Additionally, particulate filter regeneration during engine running inan HEV may be carried out during combustion of one or more cylinders,and one or more remaining non-combusting cylinders may be powered by anenergy conversion device. That is, during an “engine running”regeneration in an HEV, one or more cylinders may not be combusting, inorder to conserve fuel. In such an example, the air-fuel ratio of one ormore combusting cylinders may be set to be rich such that the overallair-fuel ratio in the exhaust is stoichiometric, and the air-fuel ratioin one or more combusting cylinders may be adjusted based on emissionsfrom the three-way catalyst. Additionally or alternatively, in an HEV,particulate filter regeneration during engine running may includeselectively adjusting engine speed in the non-combusting cylinders toincrease or decrease excess oxygen directed to the particulate filter.

Returning to FIG. 9, if the answer is yes at 902, the method 900proceeds to 908, where it is determined if the engine shutdownregeneration flag is equal to one. If the answer is no at 908, themethod may proceed to 910, where an engine shutdown without activeparticulate filter regeneration is carried out, as described above withrespect to FIG. 4. Specifically, an engine shutdown at 910 may includesetting the air-fuel ratio to about stoichiometric for one or more lastcombustions at 912, and reducing a throttle opening at 914 in order toreduce excess oxygen at the particulate filter. However, if an enginerunning regeneration is already being carried out at 908 and the answeris no at 908, the method may proceed to 916 in order to continue theregeneration, in some examples.

If the answer is yes at 908, the method 900 proceeds to 916, where it isdetermined if a particulate filter temperature is greater than a secondbaseline threshold temperature T_(THRESH2). T_(THRESH2) may be athreshold temperature that is lower than T_(THRESH) of FIG. 4 (e.g.,T_(THRESH) may be associated with controls for an engine in aconventional engine), because the temperature of a particulate filter inan HEV may be increased by a greater amount than a temperature of aparticulate filter in a conventional combustion engine, in a same amountof time after an engine shutdown request. If the answer is no at 916,method 900 may proceed to 910. In some cases, the method 900 may proceedto 910, particularly if a regeneration of the particulate filter was notalready occurring before engine shutdown conditions were met at 902.

On the other hand, if the answer is yes at 916, a particulate filterregeneration is carried out during an engine shutdown and/or after anengine shutdown, as indicated at 918. In some cases, this may includecontinuing a particulate filter regeneration that is being carried outbefore engine shutdown conditions were met at 902. Particulate filterregeneration during an engine shutdown in an HEV is described in detailwith respect to method 1000 of FIG. 10.

FIG. 10 is a flowchart illustrating a method 1000 including increasingexcess oxygen to the particulate filter during an engine shutdown in anHEV at 1002. This may include setting the air-fuel ratio to be lean inat least one cylinder for one or more last combustions at 1004, and/orincreasing a throttle opening and/or charge motion control valve at1006. Further, increasing excess oxygen at the particulate filter mayinclude increasing a ram-air flow valve opening at 1008 if the vehicleis moving. Additionally, engine speed (e.g., engine spinning speed) canbe controlled (e.g., increased, or maintained) during non-combustingengine conditions, via a motor or other energy conversion device at1010, in order to increase excess oxygen flowing to the particulatefilter. By controlling engine speed of non-combusting cylinders with amotor, fresh air can be introduced to the engine, and passed through tothe particulate filter while the engine spins but does not combust. Insome cases, this may include increasing the engine speed.

Thus, an HEV has increased flexibility over a conventional engine forcontrolling a regeneration of the particulate filter during engineshutdown because of the additional controllable parameter of enginespeed (e.g., via a motor) during non-combusting engine conditions. Insome examples, such as when it is desirable to conserve energy, athrottle opening may simply be adjusted to adjust excess oxygen at theparticulate filter in an HEV during a particulate filter regenerationand engine speed may not be adjusted. In other examples, engine speedmay be adjusted via a motor to adjust excess oxygen at the particulatefilter in an HEV. In yet further examples, a combination of throttleopening and engine speed may be used to control excess oxygen levels ata particulate filter during particulate filter regeneration, where agreater throttle opening can compensate for a lower engine speed, andvice versa.

Further, it may be desirable to adjust engine speed to control excessoxygen at the particulate filter while regenerating a particulate filterwhen the vehicle is not in motion. In contrast, if the vehicle is inmotion, it may be desirable to increase excess oxygen directed to theparticulate filter by adjusting other parameters (e.g., by adjusting aram-air flow valve in a ram-air conduit).

At 1012, method 1000 may include closing the intake and exhaust valvesof the cylinders, opening the throttle, closing the EGR wastegate, andopening a HP EGR valve, if engine combusting has stopped and acompressor is still spinning. By carrying out these controls, excessoxygen delivered to the particulate filter can be increased.Specifically, fresh air is drawn in through the intake manifold,bypasses the engine via the HP EGR circuit, and is delivered immediatelyupstream of the three-way catalyst (as shown in FIG. 1) or immediatelyupstream of the particulate filter, in other examples.

At 1014, the method 1000 may include increasing exhaust heat. This maybe accomplished by retarding spark timing of at least one cylinderduring one or more last combustions at 1016. Exhaust heat may also beincreased by increasing engine speed during engine combustingconditions, in some examples.

Another method for engine shutdown regeneration in an HEV includesspinning the engine down to rest, and waiting for a particulate filtertemperature to become sufficiently high after stopping combusting. Whenthe particulate filter temperature has exceeded a low temperaturethreshold, a motor of the HEV may be engaged to at least controlspinning of the engine to increase excess oxygen directed to theparticulate filter, and the throttle opening may, in some cases, also beincreased to increase excess oxygen. In this way, a natural increase inparticulate filter temperature upon engine shutdown is taken advantageof, and controls for increasing the particulate filter temperature canbe omitted. In such an example, the regeneration reaction is carried outat least during engine rest.

At 1018, excess oxygen levels and temperature at the particulate filtercan be controlled during the regeneration reaction by adjusting variousoperating parameters, as discussed with respect to FIG. 5 and FIG. 6.These operating parameters may include a throttle opening, an air-fuelratio, an amount of fresh ram-air supplied in the exhaust, an HP EGRvalve opening, air-fuel ratio, and spark timing, as just some examples.Furthermore, in an HEV, engine speed can be adjusted by an energyconversion device to control excess oxygen levels and particulate filtertemperature. As discussed above, engine speed may be adjusted under someconditions in an HEV (e.g., during vehicle motion) and other parametersmay be adjusted under other conditions in an HEV (e.g., during engineidling).

The adjusting of engine speed may be based on an exhaust gas oxygensensor and/or an exhaust temperature sensor. The exhaust gas oxygensensor and/or exhaust temperature sensor may provide an indication of aregeneration reaction rate, and as such, the excess oxygen directed tothe particulate filter by engine spinning may be adjusted to control theregeneration rate. Accordingly, the amount of excess oxygen directed tothe particulate filter by engine spinning may be further based on anamount of particulate at the particulate filter.

Turning now to FIG. 11, an exemplary timeline of several operatingparameters during engine running regeneration, and during a continuationof regeneration during engine shutdown in a hybrid electric vehicle, isillustrated. At t₀, the engine is combusting, excess oxygen at theparticulate filter is low, and particulate filter temperature is low,such that a regeneration reaction is not occurring. However, thetemperature is greater than T_(THRESH2) at t₀.

At t₁, a decision to perform engine running particulate filterregeneration is made. Accordingly, spark timing is nominally retarded toheat up the particulate filter. In a hybrid electric vehicle, sparktiming of one or more cylinders may be maximally, or near-maximally,retarded such that the retarded cylinder(s) are generating negligibletorque and large amounts of heat, and an energy conversion device can beused to provide desired engine torque. As such, the spark timing may bemore retarded during engine running regeneration in a hybrid electricvehicle than in engine running regeneration in a non-hybrid electricvehicle. Accordingly, a temperature threshold T_(THRESH2) referred to at916 of method 900 may be lower than the temperature threshold T_(THRESH)referred to at 416 of method 400, because more exhaust heating may becarried out by retarding a spark timing in an HEV than in a non-HEV.

Turning back to FIG. 11, at t₁, the vehicle may be moving and a ram-airflow valve opening may be increased. As a result, fresh ram-air may beintroduced upstream of the particulate filter, and excess oxygen at theparticulate filter increases after t₁. At t₂ t₂, particulate filtertemperature is within a range suitable for carrying out a regenerationreaction, and the excess oxygen is above O_(LOW), a low excess oxygenthreshold for carrying out the regeneration reaction. As a result, theregeneration reaction begins at a predetermined rate.

At t₃, engine shutdown conditions are met (e.g., battery SOC is high,engine speed and engine load are low), and an engine shutdownregeneration flag is set equal to one. In response, the air-fuel ratiois made lean at t₃ to increase excess oxygen at the particulate filter.In this example, because ram-air is being directed to the particulatefilter at a sufficient rate to maintain excess oxygen above O_(LOW) atthe particulate filter, an opening of the throttle is not increased att₃. However, the throttle opening may be increased at any point aftert₁, in other examples. Furthermore, at t₃, spark timing is maintainedretarded in order to assist in the maintenance of the particulate filtertemperature above T_(LOW).

At t₄, engine combustion stops, as indicated by the absence of anair-fuel ratio and cessation of spark timing after t₄. The engine speedis reduced to a new engine speed, which may be maintained by an energyconversion device (e.g., motor) in the hybrid electric vehicle. In orderto counteract a potential reduction in excess oxygen caused by thedecreased engine speed, throttle opening is increased at t₄, towide-open throttle (WOT). As a result, a level of excess oxygen at t₄ ismaintained, even though the engine speed is reduced.

At t₅, excess oxygen increases above O_(HIGH) and, as a result, thefilter temperature decreases as the regeneration reaction ratedecreases. In response to the increase in excess oxygen and/or decreasein filter temperature, the engine speed is reduced at t₅ to therebyreduce excess oxygen flowing to the particulate filter. This has theresult of returning the excess oxygen level at the particulate filterback into a desired range (e.g., below high excess oxygen thresholdO_(HIGH)) at t₅′, thereby increasing the regeneration reaction rate andreturning the filter temperature to the desired temperature range (e.g.,above low temperature threshold T_(LOW)). After t₅′, the regenerationreaction may proceed at the predetermined rate.

FIG. 12 illustrates a second exemplary timeline of various engineparameters during a particulate filter regeneration that is initiatedduring an engine shutdown in an HEV. At t₀, the engine is combusting,the air-fuel ratio is about stoichiometric and spark timing is MBT. Adecision to perform engine shutdown, based on engine shutdown conditionsbeing met, is made at t₁. Here, an engine running regeneration was notbeing performed prior to engine shutdown conditions being met at t₁.

In order to increase excess oxygen flowing to the particulate filter, anair-fuel ratio is made lean for one or more last combustions andthrottle opening is also increased at t₁. Accordingly, excess oxygen atthe particulate filter increases after t₁. Further, at t₁, spark timingis retarded for one or more last combustions in order to increaseexhaust heat directed at the particulate filter. This is reflected bythe increase in filter temperature between t₁ and t₂.

At t₂, the engine may stop combusting, and an energy conversion devicecoupled to the engine in the HEV may maintain the engine speed. As aresult, the increase in excess oxygen at the particulate filter maybegin to level off after t₂.

At t₃, the particulate filter temperature is within a desiredtemperature range, and the excess oxygen at the particulate filter iswithin a desired excess oxygen range. The regeneration reaction maybegin at a predetermined rate.

At t₄, the particulate filter temperature increases above a hightemperature threshold T_(HIGH). In response, the throttle opening isdecreased and the engine speed is reduced at t₄. Thereafter, particulatefilter temperature decreases due to the decrease in excess oxygen at theparticulate filter. In other words, a reduction in excess oxygen maylead to a reduction in the regeneration reaction rate, thus causing adecrease in particulate filter temperature. The regeneration reactionmay continue until the particulate filter temperature decreases belowT_(LOW), the excess oxygen decreases below O_(LOW), and/or until theregeneration reaction is substantially complete (e.g., there is a lowamount of particulate on the particulate filter), as long as theregeneration reaction is sustained by appropriate control of the variousoperating parameters discussed.

It may be appreciated that, although feedback control of excess oxygen,particulate filter temperature, regeneration reaction rate, etc. hasbeen shown in several exemplary timelines herein, feedforward orpredictive control may also be implemented.

Turning now to FIG. 13, a flowchart illustrating a method 1300 forstarting an engine is provided. Specifically, at 1302, it is determinedif start conditions are met. This may include, at least in a non-HEV, anoperator request to start, or operator tip-in after a deceleration fuelshut-off. In an HEV, start conditions may further include an enginespeed or engine load above a predetermined threshold (e.g., where amotor cannot provide sufficient torque). If the answer is no at 1302,the method 1300 may terminate.

However, if the answer is yes at 1302, the method 1300 includesestimating an amount of stored oxygen at a three-way catalyst at 1304.This estimating may include determining a backpressure in the exhaust,detected at 1306. Further, the estimating may include determining at1308 if a regeneration was performed at last engine shutdown and, if so,the duration of the last regeneration, at 1310.

A last engine shutdown may be an engine shutdown performed before thecurrent time, without any intervening engine shutdowns, such that it isan engine shutdown closest in time to the engine start. The method 1300considers whether or not a regeneration was carried out during the lastengine shutdown, in order to account for differences in stored oxygen atthe three-way catalyst during engine start. Differences in stored oxygenat the three-way catalyst may be due to differences of excess oxygenflow or excess oxygen flow rate during a particulate filter regenerationduring engine shutdown.

Accordingly, if an amount of stored oxygen at the three-way catalyst isnot greater than a threshold amount (e.g., a particulate filterregeneration was not performed on a last engine shutdown) as determinedat 1312, the method 1300 includes setting the air-fuel ratio to aboutstoichiometric, or to be lean, during an engine start at 1314. Themethod 1300 may also include setting one or more other engine operatingparameters (e.g., advancing spark timing, injection timing, and/oradjusting idle set point speed, etc.) based on the particulate filternot having been regenerated on a last engine shutdown. For example, anidle set point speed may be set to be lower than an idle set point speedfor an engine start after no particulate filter regeneration.

At 1316, the method 1300 may include further adjusting one or moreengine parameters such as air-fuel ratio, spark timing, etc., based on atemperature of the three-way catalyst while performing the engine start.

In this exemplary method, if it is determined that the amount of storedoxygen at the three-way catalyst is greater than the threshold amount at1312 (e.g., a regeneration was performed on the last engine shutdown),the method 1300 includes setting the air-fuel ratio to be rich duringthe engine start at 1318. By operating rich during the engine start,unburned fuel can be oxidized by the stored oxygen on the three-waycatalyst during the start, thus reducing a potential release of NOx tothe atmosphere. The method 1300 may also include setting, at 1318, oneor more other engine operating parameters (e.g., retarding spark timing,injection timing, and/or adjusting idle start point, etc.) based on theparticulate filter having been regenerated on a last engine shutdown.

At 1320, the method 1300 may include further adjusting engineparameters, such as air-fuel ratio, spark timing, injection timingand/or throttle opening, based on the amount of stored oxygen on thethree-way catalyst and a three-way catalyst temperature, with anobjective of reducing emissions during the engine start. For example,spark timing may be retarded if there is a threshold amount of oxygenstored at the three-way catalyst. In this way, unburned hydrocarbons mayreact with and substantially consume the excess oxygen stored at thethree-way catalyst. In other words, during an engine start following anengine shutdown, the method may include setting one or more engineparameters based on whether the particulate filter was regeneratedduring a last engine shutdown before the engine start.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The specific routines described herein may represent one or more of anynumber of processing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various acts,operations, or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedacts or functions may be repeatedly performed depending on theparticular strategy being used. Further, the described acts maygraphically represent code to be programmed into the computer readablestorage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and nonobvious combinationsand subcombinations of the various systems and configurations, and otherfeatures, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsubcombinations regarded as novel and nonobvious. These claims may referto “an” element or “a first” element or the equivalent thereof. Suchclaims should be understood to include incorporation of one or more suchelements, neither requiring nor excluding two or more such elements.Other combinations and subcombinations of the disclosed features,functions, elements, and/or properties may be claimed through amendmentof the present claims or through presentation of new claims in this or arelated application.

Such claims, whether broader, narrower, equal, or different in scope tothe original claims, also are regarded as included within the subjectmatter of the present disclosure.

1. A method for controlling regeneration of a particulate filterpositioned downstream of an engine of a vehicle, comprising: duringcombusting engine conditions, directing exhaust from the engine to athree-way catalyst and then to a particulate filter positioneddownstream of the three-way catalyst; and during non-combusting engineconditions and while the vehicle is in motion, directing fresh ram-airto the particulate filter to regenerate the particulate filter.
 2. Themethod of claim 1, where directing fresh ram-air includes adjusting aram-air flow valve based on a vehicle speed.
 3. The method of claim 2,where adjusting the ram-air flow valve includes increasing an opening ofthe ram-air flow valve as vehicle speed decreases, and increasing theopening of the ram-air flow valve as vehicle speed increases.
 4. Themethod of claim 1, further comprising during at least some combustingengine conditions and while the vehicle is in motion, closing a ram-airflow valve based on a pressure of an exhaust passage exceeding athreshold pressure value.
 5. The method of claim 1, further comprising,during at least some combusting engine conditions while the vehicle isin motion, adjusting the ram-air flow valve to direct ram-air into anexhaust passage based on a pressure of the exhaust passage being lessthan a threshold pressure value, and regenerating the particulate filterduring the at least some combusting engine conditions.
 6. The method ofclaim 5, further comprising, during regeneration of the particulatefilter during at least some combusting engine conditions, adjusting oneor more of an air-fuel oscillation amplitude, a lean duration, and arich duration in one or more combusting cylinders based on a vehiclespeed during regeneration.
 7. The method of claim 6, where adjustingincludes increasing the lean duration as the vehicle speed decreases,and increasing the rich duration as vehicle speed increases.
 8. Themethod of claim 6, where adjusting includes increasing oscillationamplitude as vehicle speed decreases.
 9. The method of claim 1, furthercomprising, during non-combusting engine conditions, controlling enginespeed with an energy conversion device coupled to the engine.
 10. Asystem for controlling regeneration of a particulate filter in avehicle, comprising: a plurality of cylinders; an emission controldevice positioned downstream of the plurality of cylinders; aparticulate filter positioned downstream of the emission control device;and an electronic controller including a computer-readable storagemedium with instructions to regenerate the particulate filter during atleast some non-combusting engine conditions and while the vehicle is inmotion by opening a ram-air flow valve to increase excess oxygendirected upstream of the particulate filter and downstream of theemission control device.
 11. The system of claim 10, where the emissioncontrol device is a three-way catalyst.
 12. The system of claim 10,further comprising an oxygen sensor positioned upstream of theparticulate filter and configured to detect an amount of excess oxygen,where the electronic controller is further configured to adjust theram-air flow valve based on the amount of excess oxygen detected at theparticulate filter.
 13. The system of claim 10, further comprising atemperature sensor positioned upstream of the particulate filter, wherethe electronic controller is further configured to adjust the ram-airflow valve based on a temperature at the particulate filter detected bythe temperature sensor.
 14. The system of claim 10, further comprisingan energy conversion device coupled to the engine, where the energyconversion device is configured to spin the plurality of cylinders, andthus control the vehicle speed.
 15. A method for controllingregeneration of a particulate filter, comprising: during non-combustingengine conditions and during vehicle motion, directing ram-air via aram-air flow valve to a position upstream of the particulate filter anddownstream of a three-way catalyst to regenerate the particulate filter;and during engine combusting conditions, adjusting the ram-air flowvalve based on whether exhaust pressure is less than a thresholdpressure value.
 16. The method of claim 15, further comprising, duringnon-combusting engine conditions, controlling an engine speed with anenergy conversion device coupled to the engine.
 17. The method of claim15, further comprising regenerating the particulate filter during thenon-combusting engine conditions and during the engine combustingconditions.
 18. The method of claim 17, where the non-combusting engineconditions follow the combusting conditions, and where the regeneratingstarts during the engine combusting conditions and continues during thenon-combusting engine conditions.
 19. The method of claim 15, furthercomprising discontinuing the ram-air flow to the particulate filterduring engine combusting conditions when the exhaust pressure is greaterthan the threshold pressure value.
 20. A method for controllingregeneration of a particulate filter in a vehicle, comprising:regenerating the particulate filter by directing ram-air to theparticulate filter during combusting engine conditions while the vehicleis in motion or during non-combusting engine conditions while thevehicle is in motion.